Plastic contamination in bio-waste anaerobic digestion systems: Understanding the role of biodegradable plastics

The separate collection of bio-waste across the European Union has positioned anaerobic digestion (AD) as a key process, enabling simultaneous energy recovery through biogas production and organic recycling through digestate application to soils. However, plastic contamination in bio-waste streams, primarily from food packaging, challenges process performance, digestate quality, and overall circularity. To mitigate conventional plastic contamination, biodegradable plastics have been proposed as alternatives in bio-waste management, yet their behavior and fate under anaerobic conditions remain uncertain. This review presents a global state-of-the-art analysis of plastic contamination in bio-waste AD, with particular emphasis on the role of biodegradable plastics. It first situates AD within the conceptual and regulatory framework of bio-waste organic recycling and summarizes key bio-waste characteristics relevant to AD. Current knowledge on the anaerobic biodegradability of biodegradable polymers is then synthesized, including strategies proposed to enhance degradation, providing a basis for analyzing experimental studies on commercially available biodegradable plastic products with respect to biodegradability, process stability, energy performance, and microbial community dynamics. The review further examines plastic contamination in AD systems by synthesizing reported contamination levels in bio-waste streams and digestates for both macro- and microplastics derived from conventional and biodegradable polymers. Analytical methodologies used to characterize this contamination are critically assessed, with attention to their suitability and limitations for complex organic matrices and biodegradable plastics. Finally, the environmental implications of digestate land application are discussed, and key research perspectives are identified to clarify the role of biodegradable plastics and advance circularity in bio-waste AD systems.